The present invention relates to a semiconductor switching circuit, and more particularly to a semiconductor switching circuit by means of which a drive circuit for a thyristor can operate at low power consumption.
A conventional technique for such a thyristor drive circuit is described, for example, in Japanese Patent Laid-Open Publication JP-A-59-14355. According to this technique, a transistor whose collector and emitter are connected across the gate and cathode of a thyristor, is controlled a short-circuit the gate-cathode path and turn off the thyristor.
Such conventional technique, however, does not consider the amount of drive current for turning off a thyristor. Namely, as the turn-off current of the thyristor increases, the base current of the transistor for short-circuiting the gate-cathode path of the thyristor, i.e., the turn-off drive current for the thyristor, also increases. Thus, there arises a problem that a large drive power is required.